JP7159621B2 - VOLTAGE GENERATOR, POWER CONTROL DEVICE, IMAGE FORMING APPARATUS, AND CONTROL METHOD - Google Patents

Description

The present invention relates to a voltage generator, a power supply controller, an image forming apparatus, and a control method.

Conventionally, in an electrophotographic image forming apparatus such as a digital multi-function machine, a charging roller (rotating body) is brought close to the surface of a photoreceptor, and a high voltage generated by a voltage generator is applied to the charging roller. The body surface is uniformly charged to a predetermined potential.

As such a voltage generator, there is known a system in which a DC power supply and an AC power supply connected to the DC power supply are provided, and a voltage obtained by superimposing an AC voltage on the DC voltage is generated and applied to the charging roller (Patent Reference 1).

In such a method, the potential on the surface of the photoreceptor becomes equal to the DC component of the applied voltage, and the potential on the surface of the photoreceptor can be controlled by adjusting the DC voltage.

However, in such an image forming apparatus, if there is a change in the load of the image forming parts or the like to which the voltage is applied from the voltage generator, the DC component of the output voltage of the voltage generator will not be constant, and the surface of the photoreceptor will not be constant. Electrification is no longer uniform. As a result, an abnormal image such as color unevenness is generated. Specifically, when the charging roller and the photosensitive member, which are image forming parts, are distorted and the gap between the charging roller and the photosensitive member is changed, the load resistance and the like fluctuate and the load current changes. Due to this load current fluctuation, the waveform of the AC component of the output voltage output from the voltage generator becomes asymmetrical between the positive and negative sides. As a result, the DC component of the output voltage fluctuates, the voltage applied to the charging roller fluctuates, and an abnormal image occurs.

The technology disclosed has been made to solve this problem in view of the above circumstances, and aims to suppress fluctuations in the DC component of the output voltage due to load fluctuations.

The disclosed technology is a voltage generator that has a DC power supply and an AC power supply connected to the DC power supply, generates a voltage obtained by superimposing an AC voltage on a DC voltage, and applies the voltage to a rotating body, Variation in voltage effective value calculated for each cycle of the voltage waveform of the output voltage of the AC power supply, current effective value calculated for each cycle of the voltage waveform of the output current of the AC power supply, or current waveform of the output current A fluctuation phase determination unit that determines whether or not the fluctuation of either one of the current peak value obtained by adding the positive current peak value and the negative current peak value detected based on is in opposite phase, and the fluctuation phase determination unit When the determination result is in reverse phase, the proportional gain in PI control or the reference voltage is calculated from the positive current effective value and the negative current effective value calculated from the output current, and the determination result by the fluctuation phase determination unit and a voltage control unit that performs control to set the proportional gain or the reference voltage to a specified value when the V and V are not in opposite phase .

Fluctuations in the DC component of the output voltage due to load fluctuations can be suppressed.

1 is a diagram showing a schematic configuration of an image forming apparatus; FIG. It is a figure which shows the structure of the voltage generator of 1st Embodiment. 4 is a diagram showing a configuration of a voltage control section; FIG. FIG. 4 is a diagram showing a specific circuit example of a power supply unit; It is a figure which shows the equivalent circuit of a power supply part. FIG. 4 is a diagram showing the relationship between the load current flowing through the load resistor and the amount of voltage drop; FIG. 5 is a diagram illustrating current waveform fluctuations when load fluctuations occur; FIG. 10 is a diagram illustrating variations in voltage waveform when a load variation occurs; FIG. 10 is a diagram showing time fluctuations of output current and output voltage when fluctuations occur due to current due to load fluctuations; FIG. 10 is a diagram showing temporal fluctuations in output current and output voltage when fluctuations occur due to voltage; 4 is a flowchart for explaining the operation of the voltage generator; 4 is a flowchart for explaining the operation of a static variation measuring unit; FIG. 3 is a diagram illustrating waveforms of an output current and an output voltage from a conventional voltage generator; 4 is a diagram illustrating waveforms of an output current and an output voltage from the voltage generator of the first embodiment; FIG. 4 is a graph showing the relationship between variable voltage and load current; It is a figure which shows the structure of the power supply control part of 2nd Embodiment. FIG. 13 is a diagram showing the configuration of a voltage control unit according to a third embodiment; FIG. It is a figure which shows the structure of the power supply control part of 4th Embodiment.

<First embodiment>
A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an electrophotographic image forming apparatus 100. As shown in FIG.

In FIG. 1, an image forming apparatus 100 includes a voltage generating device 10, a photoreceptor 2, a charging roller 3, an exposure section 4, a developing device 5, a primary transfer roller 6, an intermediate belt 7, a static eliminator 8, and a high voltage power supply 9. . The voltage generator 10 has a power supply section 11 and a power control section (power control device) 12 . The power supply unit 11 includes a DC power supply 11b and an AC power supply 11a connected to the DC power supply 11b.

The charging roller 3 is a rotating body arranged close to the surface of the drum-shaped photoreceptor 2 . A gap between the charging roller 3 and the photoreceptor 2 is, for example, several tens of micrometers.

The power control unit 12 controls the operations of the AC power supply 11a and the DC power supply 11b, and causes the power supply unit 11 to generate a voltage in which the AC voltage is superimposed on the DC voltage. The frequency of this alternating voltage is, for example, about 2 kHz. The DC voltage is a negative voltage, eg -700V.

A voltage generated by the power supply unit 11 is applied to the charging roller 3 . When a voltage is applied to the charging roller 3, discharge occurs between the surface of the photoreceptor 2 and the surface of the charging roller 3, and the surface of the photoreceptor 2 is charged to a predetermined potential.

The exposure unit 4 exposes the charged surface of the photoreceptor 2 according to an image signal. This exposure forms an electrostatic latent image on the photoreceptor 2 . A developing device 5 develops a toner image on the photoreceptor 2 . A high voltage power supply 9 applies a high voltage to the primary transfer roller 6 . The toner image on the photosensitive member 2 is transferred to the intermediate belt 7 by applying a high voltage to the primary transfer roller 6 .

The toner image transferred to the intermediate belt 7 is transferred to a recording material by a secondary transfer portion, and then fixed by a fixing means to form an image. The static eliminator 8 removes charges on the surface of the photoreceptor 2 by irradiating it with light. After that, the surface of the photoreceptor 2 is charged again.

In the case of color printing, there are four similar configurations, each of which transfers a toner image to an intermediate belt for each color, and then reaches a secondary transfer section and fixing means.

FIG. 2 is a diagram showing the configuration of the voltage generator 10 of the first embodiment. 2, the power supply control unit 12 included in the voltage generator 10 includes a voltage effective value calculation unit 30, a current effective value calculation unit 31, an averaging unit 32, a fluctuation phase determination unit 33, a correction coefficient calculation unit 34, a correction coefficient It has a setting section 35 , a voltage control section 36 and a static variation measurement section 37 . The voltage generator 10 also includes a first full-wave rectifier circuit 40 , a DC component removal circuit 41 , and a second full-wave rectifier circuit 42 .

The first full-wave rectifier circuit 40 full-wave rectifies the AC component of the output voltage output from the power supply unit 11 and outputs a full-wave rectified voltage waveform. The voltage effective value calculator 30 calculates the voltage effective value Vrms based on the full-wave rectified voltage waveform input from the first full-wave rectifier circuit 40 . Here, the voltage effective value Vrms is represented by the following formula (1). V(t) represents a voltage waveform. T represents the period of the voltage waveform.

電圧実効値算出部３０は、周期Ｔごとに電圧実効値Ｖｒｍｓを算出して出力する。

The voltage effective value calculator 30 calculates and outputs the voltage effective value Vrms for each cycle T. FIG.

The DC component removing circuit 41 removes the DC component from the output current output from the power supply unit 11 and outputs the current from which the DC component has been removed. The second full-wave rectifier circuit 42 full-wave rectifies the current output from the DC component removal circuit 41 and outputs a full-wave rectified current waveform. The current effective value calculator 31 calculates the current effective value Irms based on the full-wave rectified current waveform input from the second full-wave rectifier circuit 42 . Here, the current effective value Irms is represented by the following formula (2). I(t) represents the current waveform.

電流実効値算出部３１は、正電流実効値算出部３１ａ、負電流実効値算出部３１ｂ、及び加算部３１ｃにより構成される。正電流実効値算出部３１ａは、直流成分除去回路４１により直流成分が除去された電流のうちの正電流の実効値である正電流実効値Ｉｐｒｍｓを算出する。負電流実効値算出部３１ｂは、直流成分除去回路４１により直流成分が除去された電流のうちの負電流の実効値である負電流実効値Ｉｎｒｍｓを算出する。ここで、正電流実効値Ｉｐｒｍ及び負電流実効値Ｉｎｒｍｓは、それぞれ下式（３）及び下式（４）で表される。

The current effective value calculator 31 includes a positive current effective value calculator 31a, a negative current effective value calculator 31b, and an adder 31c. The positive current effective value calculator 31 a calculates the positive current effective value Iprms, which is the effective value of the positive current in the current from which the DC component has been removed by the DC component removal circuit 41 . The negative current effective value calculator 31b calculates a negative current effective value Inrms, which is the effective value of the negative current in the current from which the DC component has been removed by the DC component removal circuit 41 . Here, the positive current effective value Iprm and the negative current effective value Inrms are represented by the following equations (3) and (4), respectively.

正電流実効値算出部３１ａ及び負電流実効値算出部３１ｂは、それぞれ周期Ｔごとに正電流実効値Ｉｐｒｍｓ及び負電流実効値Ｉｎｒｍｓを算出して出力する。

The positive current effective value calculator 31a and the negative current effective value calculator 31b calculate and output the positive current effective value Iprms and the negative current effective value Inrms for each cycle T, respectively.

The addition unit 31c adds the positive current effective value Iprms output from the positive current effective value calculation unit 31a and the negative current effective value Inrms calculated by the negative current effective value calculation unit 31b to obtain the above-mentioned current effective value Irms. calculate. That is, the current effective value calculator 31 calculates and outputs the current effective value Irms for each cycle T.

The averaging section 32 is composed of a first averaging section 32a and a second averaging section 32b. The first averaging unit 32a averages the voltage effective value Vrms output from the voltage effective value calculating unit 30 for each averaging period Tc, which is a constant period, to calculate an average voltage effective value AVG (Vrms). The second averaging unit 32b averages the current effective value Irms output from the current effective value calculating unit 31 for each averaging period Tc to calculate an average current effective value AVG (Irms). Here, the average voltage effective value AVG (Vrms) and the average current effective value AVG (Irms) are represented by the following equations (5) and (6), respectively. n represents the number of cycles corresponding to the averaging cycle Tc. That is, n corresponds to the reciprocal of the averaging period Tc. Vrms(i) represents the voltage effective value Vrms in cycle i. Irms(i) represents the current effective value Irms in cycle i. Note that one cycle corresponds to one cycle T.

平均化周期Ｔｃは、予め電源制御部１２に含まれる記憶部に記憶されている。平均化周期Ｔｃは、負荷電流の変動周期、すなわち、作像部品である帯電ローラ３や感光体２の径に基づいて算出される。ここでは、計算の簡単化のため、インダクタンスノイズ等の変動要因は無視する。負荷変動の周期は、感光体２より径が小さい帯電ローラ３の径に基づいて計算することが好ましい。例えば、帯電ローラ３の円周を４０ｍｍ、線速度を３５２．８ｍｍ／ｓとすると、負荷変動の周期は、４０／３５２．８≒１１３ｍｓとなる。平均化周期Ｔｃを負荷変動の周期の１／１０倍と設定すると、Ｔｃ＝１１．３ｍｓとなる。

The averaging period Tc is stored in advance in the storage section included in the power supply control section 12 . The averaging period Tc is calculated based on the fluctuation period of the load current, that is, the diameters of the charging roller 3 and the photosensitive member 2, which are image forming parts. Here, to simplify the calculations, fluctuation factors such as inductance noise are ignored. It is preferable to calculate the period of load fluctuation based on the diameter of the charging roller 3 which is smaller in diameter than the photosensitive member 2 . For example, if the circumference of the charging roller 3 is 40 mm and the linear velocity is 352.8 mm/s, the period of load fluctuation is 40/352.8≈113 ms. If the averaging period Tc is set to be 1/10 times the period of the load fluctuation, Tc=11.3 ms.

Assuming that the period T, which is the effective value calculation period, is 0.5 ms, the number of cycles n for the above averaging is n=11.3/0.5≈23.

The first averaging unit 32a and the second averaging unit 32b, for example, calculate and output the average voltage effective value AVG (Vrms) and the average current effective value AVG (Irms) for each averaging period Tc. Note that the averaging period Tc is not limited to the value obtained by the above calculation method.

Fluctuation phase determination unit 33 determines whether or not the time variation (variation over time) of voltage effective value Vrms and the time variation of current effective value Irms are in opposite phase. Specifically, the fluctuation phase determination unit 33 calculates the voltage phase fluctuation amount Vph and the current phase fluctuation amount Iph for each averaging period Tc. Here, the voltage phase fluctuation amount Vph and the current phase fluctuation amount Iph are expressed by the following expressions (7) and (8), respectively. AVG(Vrms)' is the average voltage effective value output last time from the first averaging unit 32a. AVG(Irms)' is the average current effective value output last time from the second averaging unit 32b.

Vph=AVG(Vrms)-AVG(Vrms)' (7)
Iph=AVG(Irms)-AVG(Irms)' (8)
Time fluctuations in the voltage effective value Vrms and the current effective value Irms are caused by the load fluctuations described above, but these time fluctuations have a longer cycle than the effective value calculation cycle. Therefore, the fluctuation phase determination unit 33 determines the voltage phase fluctuation amount Vph and the current phase based on the average voltage rms value AVG (Vrms) and the average current rms value AVG (Irms) instead of the voltage rms value Vrms and the current rms value Irms. The fluctuation amount Iph is calculated.

In addition, the fluctuation phase determination unit 33 determines the magnitude relationship based on the previous output value AVG (Vrms)' of the average voltage effective value AVG (Vrms) output from the first averaging unit 32a, and the second averaging unit If the average current effective value AVG (Irms) output from 32b is different from the previous output value AVG (Irms)' as a reference, it is determined that the fluctuation phase is the opposite phase. Specifically, the fluctuation phase determination unit 33 determines that the fluctuation phase is the opposite phase when "Vph>0 and Iph<0" is satisfied, or when "Vph<0 and Iph>0" is satisfied. do.

The correction coefficient calculator 34 includes an output impedance storage unit 34a, a first correction coefficient calculator 34b, and a second correction coefficient calculator 34c. The output impedance storage section 34a stores the output impedance Z of the power supply section 11. FIG. The first correction coefficient calculation unit 34b calculates the first correction coefficient αp based on the positive current effective value Iprms output from the positive current effective value calculation unit 31a and the output impedance Z stored in the output impedance storage unit 34a. calculate. The second correction coefficient calculation unit 34c calculates the second correction coefficient αn based on the negative current effective value Inrms output from the negative current effective value calculation unit 31b and the output impedance Z stored in the output impedance storage unit 34a. calculate.

Specifically, the first correction coefficient calculator 34b and the second correction coefficient calculator 34c calculate the first correction coefficient αp and the second correction coefficient αn based on the following equations (9) and (10), respectively. do. Here, k is the static variation amount measured by the static variation amount measuring section 37 .

αp=Z×Irms−k (9)
αn=Z×Inrms−k (10)
The correction coefficient setting unit 35 sets a correction coefficient for gain correction of the output voltage of the power supply unit 11 based on the determination result of the fluctuation phase by the fluctuation phase determination unit 33 . Specifically, the correction coefficient setting unit 35 sets the positive voltage correction coefficient gp as the first correction coefficient Let the correction coefficient gn be the second correction coefficient αn. On the other hand, the correction coefficient setting unit 35 sets gp=0 and gn=0 when the fluctuation phase is not the opposite phase. The positive voltage correction coefficient gp is a correction coefficient for performing gain correction on the positive voltage component (positive phase component) of the output voltage of the AC power supply 11a. The negative voltage correction coefficient gn is a correction coefficient for correcting the negative voltage component (negative phase component) of the output voltage.

The voltage control section 36 feedback-controls the output voltage of the power supply section 11 based on the positive voltage correction coefficient gp and the negative voltage correction coefficient gn.

Although the details will be described later, the static variation amount measuring unit 37 operates at the time of shipping inspection or the like, and detects the maximum and minimum values of the positive peak value of the output voltage to determine the static variation amount k. It is measured and supplied to the correction coefficient calculator 34 . The static fluctuation amount k is the amount of voltage fluctuation caused by the voltage generator 10 itself in a constant load state.

FIG. 3 is a diagram showing the configuration of the voltage control section 36. As shown in FIG. 3, the voltage control section 36 includes a reference voltage generation section 50, a subtractor 51, a proportional section 52, an integration section 53, a first adder 54, a reference sine wave generation section 55, a first multiplier 56, and an offset value storage. It has a section 57 , a second adder 58 , a PWM (Pulse Width Modulation) signal generation section 59 , a timer 60 and a positive/negative determination section 61 . The proportional section 52, the integrating section 53, and the first adder 54 constitute a PI control section.

The voltage control unit 36 receives the voltage effective value Vrms from the voltage effective value calculation unit 30 described above. The reference voltage generator 50 generates a reference voltage. The subtractor 51 inputs a value obtained by subtracting the reference voltage from the voltage effective value Vrms to the proportional section 52 and the integrating section 53 included in the PI control section as a command input value. The proportional part 52 proportionally controls the command input value with a proportional gain Kp. The integration unit 53 integrates the command input value with the integration gain Ki. The first adder 54 adds the output value of the proportional section 52 and the output value of the integrating section 53 and outputs the result.

The reference sine wave generator 55 generates and outputs a reference sine wave. The frequency of this reference sine wave is, for example, 2 kHz. The first multiplier 56 multiplies the output value from the first adder 54, which is the output value from the PI control section, by the reference sine wave output from the reference voltage generation section 50, and outputs the result. The offset value storage unit 57 stores an offset value caused by a switching circuit included in the AC power supply 11a, which will be described later. The second adder 58 adds the offset value stored in the offset value storage unit 57 to the output value from the first multiplier 56 and outputs the result.

The PWM signal generator 59 generates a PWM signal and supplies it to the driver circuit of the AC power supply 11a. The driver circuit generates a drive signal (ON/OFF signal) and inputs it to the switching circuit.

The timer 60 supplies the clock signal to the PWM signal generator 59 .

The positive/negative determination unit 61 determines whether the voltage is positive or negative based on the reference sine wave generated by the reference voltage generation unit 50 . Specifically, the positive/negative determination unit 61 determines that the voltage is positive when the phase of the reference sine wave is positive (0° or more and less than 180°), and the phase of the reference sine wave is negative (180° or more and less than 360°). ), the voltage is determined to be negative. Further, the positive/negative determination unit 61 receives the positive voltage correction coefficient gp and the negative voltage correction coefficient gn as correction coefficients from the correction coefficient setting unit 35 described above. The positive/negative determination unit 61 selects and outputs the positive voltage correction coefficient gp when the voltage of the reference sine wave is positive, and selects the negative voltage correction coefficient gn when the voltage of the reference sine wave is negative. output.

Next, details of the proportional part 52 will be described. The proportional section 52 has a reference proportional gain storage section 62 , a third adder 63 and a second multiplier 64 . The reference proportional gain storage unit 62 stores the value of the reference proportional gain Kpa.

The third adder 63 adds the positive voltage correction coefficient gp or the negative voltage correction coefficient gn output from the positive/negative determination unit 61 to the reference proportional gain Kpa stored in the reference proportional gain storage unit 62 to obtain a reference proportional gain. Correct the gain Kpa. This corrected reference proportional gain Kpa is used for proportional control as the aforementioned proportional gain Kp. Specifically, when the voltage of the reference sine wave is positive, Kp=Kpa+gp, and when the voltage of the reference sine wave is negative, Kp=Kpa+gn. The second multiplier 64 multiplies the command input value described above by the proportional gain Kp output from the third adder 63 .

FIG. 4 is a diagram showing a specific circuit example of the power supply unit 11. As shown in FIG. In FIG. 4, the AC power supply 11a includes a first transistor Q1 and a second transistor Q2 that form a half bridge circuit as a switching circuit. A drive signal is input to the first transistor Q1 and the second transistor Q2 from the driver circuit described above. The DC power supply 11b includes a third transistor Q3 to which a PWM signal for adjusting the DC voltage is input.

The first full-wave rectifier circuit 40 described above includes a diode D1, resistors R1 and R2, and a capacitor C1. The voltage full-wave rectified by the first full-wave rectifier circuit 40 is output from the terminal 70 to the voltage control section 36 . The DC component removal circuit 41 described above includes a capacitor C2. The second full-wave rectifier circuit 42 described above includes a diode D2, resistors R3 and R4, and a capacitor C4. The current full-wave rectified by the second full-wave rectifier circuit 42 is output from the terminal 71 to the voltage control section 36 .

The AC power supply 11a shown in FIG. 4 has three large resistance components, namely, the ON resistance Ron of the first transistor Q1 or the second transistor Q2, the DC resistance Rl of the resistor R5, and the output resistance Ro of the resistor R6. For example, the series impedance Z=Ron+Rl+Ro is stored as the output impedance Z in the output impedance storage section 34a.

FIG. 5 is a diagram showing an equivalent circuit of the power supply section 11. As shown in FIG. In FIG. 5, load resistance R is a combination of the three resistance components shown in FIG. The load is a load resistance caused by the charging roller 3 and the photoreceptor 2, which are image forming parts. Due to the distortion of the charging roller 3 and the photosensitive member 2 and the variation of the gap between the charging roller 3 and the photosensitive member 2, the load resistance changes and the load current (the positive current Ip and the negative current In) changes. Here, the positive current Ip is the load current when the output voltage of the AC power supply 11a is positive (positive phase). The negative current In is the load current when the output voltage of the AC power supply 11a is negative (negative phase).

When the load current flows through the load resistor R, a voltage drop occurs. As the load current increases or decreases, the amount of voltage drop changes and the output voltage from the power supply section 11 fluctuates. Since the DC component of the output voltage output from the power supply unit 11 is not zero, the positive current Ip and the negative current In flowing through the load resistor R are different. For example, when the DC component of the output voltage is negative, the magnitude of the positive current Ip is smaller than the magnitude of the negative current In.

Next, details of the reason why the DC component of the output voltage of the power supply unit 11 fluctuates due to load fluctuation will be described with reference to FIGS. 6 to 8. FIG. FIG. 6 is a diagram showing the relationship between the load current flowing through the load resistor R shown in FIG. 5 and the amount of voltage drop. FIG. 7 is a diagram illustrating current waveform fluctuations when load fluctuations occur. FIG. 8 is a diagram illustrating variations in voltage waveforms when load variations occur.

As shown in FIG. 7, when the positive current Ip fluctuates from I1p to I2p due to load fluctuation, the voltage fluctuates from V1p to V2p as shown in FIG. 8 according to the relationship between voltage and current shown in FIG. . As shown in FIG. 7, when the negative current In changes from I1n to I2n due to load fluctuation, the voltage changes from V1n to V2n as shown in FIG. 8 according to the relationship between the voltage and the current shown in FIG. fluctuate. Due to the difference between the amount of variation ΔVp and the amount of variation ΔVn, the DC component of the output voltage consequently varies from V1dc to V2dc. Fluctuations in this DC component cause abnormal images.

As can be understood from FIGS. 6 to 8, in the fluctuation of the output of the power supply unit 11 caused by the load fluctuation, the direction of voltage fluctuation is opposite to the direction of current fluctuation.

FIG. 9 is a diagram showing time fluctuations of the output current and the output voltage when fluctuations occur due to current due to load fluctuations. FIG. 10 is a diagram showing temporal fluctuations in the output current and the output voltage when fluctuations occur due to voltage.

As shown in FIG. 9, when a change occurs due to a current caused by a load change, the output current and the output voltage have opposite phases over time. On the other hand, as shown in FIG. 10, when fluctuations occur due to voltage, the temporal fluctuations of the output current and the output voltage are in phase. This voltage-induced variation is caused by noise in the voltage generator 10 itself, an abnormality in the control system, or the like. In the present embodiment, it is determined whether or not the time variations of the output current and the output voltage are in opposite phases in order to determine whether or not the variation is due to the current caused by the load variation. Although FIG. 9 shows the time fluctuations of the output current, the output voltage, and the effective value, the frequency of these time fluctuations is actually about 10 Hz, which is much lower than 2 kHz, which is the frequency of the output voltage. .

Next, the operation of the voltage generator 10 of this embodiment will be described. FIG. 11 is a flow chart for explaining the operation of the voltage generator 10. FIG.

First, output of a voltage in which an AC voltage is superimposed on a DC voltage is started from the power supply unit 11 (step S100). Then, the effective voltage value Vrms and the effective current value Irms are calculated by the effective voltage value calculation unit 30 and the effective current value calculation unit 31 based on the above equations (1) and (2) (step S101). Here, the current effective value Irms is calculated by the positive current effective value Iprms calculated by the positive current effective value calculation unit 31a based on the above equation (3), and by the negative current effective value calculation unit 31b by the above equation (4). and the negative current effective value Inrms calculated based on is added by the adder 31c.

The voltage rms value Vrms and the current rms value Irms are averaged by the averaging unit 32 based on the above formulas (5) and (6), respectively, and the average voltage rms value AVG (Vrms) and the average current rms value AVG (Irms) is calculated (step S102).

Then, the voltage phase fluctuation amount Vph and the current phase fluctuation amount Iph are calculated by the fluctuation phase determination unit 33 based on the above equations (7) and (8) (step S103). Further, the variation phase determination unit 33 determines whether or not the time variation of the voltage effective value Vrms and the time variation of the current effective value Irms are in opposite phase (step S104).

When the fluctuation phase is the opposite phase (step S104: YES), the correction coefficient calculator 34 calculates the first correction coefficient αp and the second correction coefficient αn (step S105). Here, the first correction coefficient αp is calculated based on the above equation (9). The second correction coefficient αn is calculated based on Equation (10) above. The calculated first correction coefficient αp and second correction coefficient αn are set as a positive voltage correction coefficient gp and a negative voltage correction coefficient gn, respectively, by the correction coefficient setting unit 35 (step S106).

On the other hand, when the fluctuation phase is not the opposite phase (step S104: NO), the correction coefficient setting unit 35 sets the positive voltage correction coefficient gp and the negative voltage correction coefficient gn to "0" (step S107).

The positive voltage correction coefficient gp and the negative voltage correction coefficient gn are supplied to the voltage control unit 36. In the voltage control unit 36, the positive/negative determination unit 61 determines the phase of the reference sine wave generated by the reference voltage generation unit 50. , is determined whether the voltage of the reference sine wave is positive or negative (step S108). When the voltage of the reference sine wave is positive, the positive/negative determination unit 61 supplies the positive voltage correction coefficient gp to the third adder 63 to add the positive voltage correction coefficient gp to the reference proportional gain Kpa ( step S109). On the other hand, when the voltage of the reference sine wave is negative, the positive/negative determination unit 61 adds the negative voltage correction coefficient gn to the reference proportional gain Kpa by supplying the negative voltage correction coefficient gn to the third adder 63. (step S110).

Then, the PI control unit performs PI control using the value obtained by adding the positive voltage correction coefficient gp or the negative voltage correction coefficient gn to the reference proportional gain Kpa as the proportional gain Kp (step S111). After that, the process returns to step S100, and the same processing is repeatedly performed.

Next, the operation of the static variation measuring section 37 will be described. FIG. 12 is a flow chart for explaining the operation of the static variation measuring section 37. As shown in FIG. The static variation measuring unit 37 is operated in a state where load variation does not occur, such as at the time of shipping inspection.

First, the power supply unit 11 starts outputting a voltage in which an AC voltage is superimposed on a DC voltage (step S200). Next, the static variation measuring unit 37 has a peak hold circuit, and detects and holds the maximum positive peak value Vpmax and the minimum positive peak value Vpmin of the output voltage output from the power supply unit 11. (step S201). Then, the static variation amount measuring unit 37 calculates the static variation amount k by subtracting the minimum value Vpmin from the maximum value Vpmax (step S202), and stores the calculated static variation amount k (step S203). .

Next, the effects of the image forming apparatus 100 of this embodiment will be described. FIG. 13A is a diagram illustrating an output current waveform from a conventional voltage generator. FIG. 13B is a diagram illustrating an output voltage waveform from a conventional voltage generator. In the conventional voltage generator, the output current fluctuates as shown in FIG. 13(A) due to the above-described load fluctuation. Since the output voltage is biased, the positive and negative AC components of the output current have different amounts of current. As the amount of voltage drop fluctuates due to the increase or decrease in the output current, the waveform of the AC component of the output voltage is distorted and becomes asymmetrical between the positive and negative sides, as shown in FIG. 13(B). As a result, the DC voltage component of the output voltage from the voltage generator fluctuates, and the surface potential of the photosensitive member 2 fluctuates. As a result, the image forming apparatus generates an abnormal image including color unevenness.

FIG. 14A is a diagram illustrating an output current waveform from the voltage generator 10 of this embodiment. FIG. 14B is a diagram illustrating an output voltage waveform from the voltage generator 10 of this embodiment. The output current waveform shown in FIG. 14(A) is the same as the conventional one, and increases and decreases due to load fluctuations. In the present embodiment, it is determined whether or not the voltage waveform variation is due to load variation by determining whether or not the time variation of the voltage effective value and the current effective value are in opposite phases. Then, when the fluctuation of the voltage waveform is caused by the load fluctuation, the output voltage gain is obtained by using the first correction coefficient αp and the second correction coefficient αn calculated based on the positive current effective value and the negative current effective value. to correct. As a result, as shown in FIG. 14B, the waveform distortion of the AC component of the output voltage is suppressed. As a result, fluctuations in the DC voltage component of the output voltage from the voltage generator 10 are suppressed, and the surface potential of the photoreceptor 2 becomes uniform. As a result, the image forming apparatus 100 suppresses the occurrence of abnormal images including color unevenness.

The gain control described above corresponds to the control of stabilizing the output voltage Vo by controlling the variable voltage Vi based on the value of the load current (positive current Ip and negative current In) in the equivalent circuit shown in FIG. As shown in FIG. 15, for example, when the load current varies from I0 to I1, the output voltage Vo is kept constant by changing the variable voltage Vi to Vi1 by gain correction. Similarly, when the load current fluctuates from I0 to I2, the output voltage Vo is kept constant by changing the variable voltage Vi to Vi2 by gain correction.

In the image forming apparatus 100 of the present embodiment, the correction coefficient setting unit 35 sets gp=0 and gn=0 when the fluctuation phase is not the opposite phase. may be used to set gp=-k and gn=-k.

Further, in the present embodiment, the first correction coefficient calculator 34b calculates the first correction coefficient αp based on the positive current effective value Iprms, but is not limited to this, and the positive current effective value Iprms is averaged. The first correction coefficient αp may be calculated based on the value averaged over the period Tc. Similarly, the second correction coefficient calculator 34c may calculate the second correction coefficient αn based on a value obtained by averaging the negative current effective values Inrms over the averaging cycle Tc.

<Second embodiment>
Next, an image forming apparatus according to the second embodiment will be described. In the voltage generator 10a included in the image forming apparatus of the second embodiment, a power control unit 12a having the configuration shown in FIG. 16 is used instead of the power control unit 12 having the configuration shown in FIG. The power supply control unit 12 a has a current peak value detection unit 80 instead of the current effective value calculation unit 31 . Other constituent parts are the same as in the first embodiment. Components similar to those of the first embodiment are denoted by the same reference numerals, and descriptions thereof are omitted.

The current peak value detection section 80 is composed of a positive current peak value detection section 80a and a negative current peak value detection section 80b. The positive current peak value detection unit 80a detects the positive current peak value Ipp during one period T based on the current waveform input from the second full-wave rectifier circuit 42 and subjected to full-wave rectification. The negative current peak value detection unit 80b detects the negative current peak value Inp during one cycle T based on the full-wave rectified current waveform input from the second full-wave rectifier circuit 42 .

In this embodiment, the positive current peak value Ipp detected by the positive current peak value detecting section 80a is input to the addition section 31c instead of the positive current effective value Iprms. Similarly, the negative current peak value Inp detected by the negative current peak value detection section 80b is input to the addition section 31c instead of the negative current effective value Inrms.

In this embodiment, the adder 31c calculates the current peak value Ips by adding the positive current peak value Ipp and the negative current peak value Inp. That is, the current peak value detection unit 80 outputs the current peak value Ips every cycle T. The current peak value Ips output from the current peak value detection unit 80 is input to the second averaging unit 32b instead of the current effective value Irms. The second averaging section 32b averages the current peak values Ips input from the current peak value detecting section 80 over a predetermined averaging period Tc to calculate an average current peak value AVG (Ips).

Phase determination by the fluctuation phase determination unit 33 is the same as in the first embodiment except that the average current peak value AVG (Ips) is used instead of the average current effective value AVG (Irms).

Also, the positive current peak value Ipp detected by the positive current peak value detection section 80a is input to the first correction coefficient calculation section 34b. Also, the negative current peak value Inp detected by the negative current peak value detection section 80b is input to the second correction coefficient calculation section 34c. In the present embodiment, the first correction coefficient calculator 34b and the second correction coefficient calculator 34c calculate the first correction coefficient αp and the second correction coefficient αn based on the following equations (11) and (12), respectively. do.

αp=Z×Ipp−k (11)
αn=Z×Inp−k (12)
Also in the present embodiment, as in the first embodiment, the waveform distortion of the AC component of the output voltage due to load fluctuations is suppressed. As a result, fluctuations in the DC voltage component of the output voltage from the voltage generator 10a are suppressed, the surface potential of the photosensitive member 2 becomes uniform, and the occurrence of abnormal images is suppressed.

In the present embodiment, for voltage, the voltage effective value calculation unit 30 calculates the voltage effective value Vrms, but similarly to the current, the voltage peak value is detected instead of the voltage effective value calculation unit 30. A voltage peak value calculator may be provided.

<Third Embodiment>
Next, an image forming apparatus according to the third embodiment will be described. In the image forming apparatus of the third embodiment, a voltage control section 36a configured as shown in FIG. 17 is used instead of the voltage control section 36 configured as shown in FIG. The voltage control section 36a is provided with a proportional section 52a in place of the proportional section 52, and the second multiplier 82 is provided between the reference voltage generating section 50 and the subtractor 51 in the first embodiment. is different from the voltage control unit 36 of . Other constituent parts are the same as in the first embodiment. Components similar to those of the first embodiment are denoted by the same reference numerals, and descriptions thereof are omitted.

The proportional part 52a proportionally controls the command input value with a proportional gain Kp. In this embodiment, the correction coefficients (the positive voltage correction coefficient gp and the negative voltage correction coefficient gn) are not input from the positive/negative determination unit 61 to the proportional unit 52a. That is, unlike the first embodiment, the proportional gain Kp is not corrected in this embodiment.

In this embodiment, the positive/negative determination unit 61 inputs the positive voltage correction coefficient gp or the negative voltage correction coefficient gn to the second multiplier 82 depending on whether the voltage of the reference sine wave generated by the reference voltage generation unit 50 is positive or negative. do. Specifically, when the voltage of the reference sine wave is positive, the positive/negative determination unit 61 selects the positive voltage correction coefficient gp and inputs it to the second multiplier 82, and when the voltage of the reference sine wave is negative, , the negative voltage correction coefficient gn is selected and input to the second multiplier 82 .

The second multiplier 82 multiplies the reference voltage generated by the reference voltage generating section 50 by the correction coefficient input from the positive/negative determining section 61 and supplies the result to the subtractor 51 . Specifically, when the voltage of the reference sine wave is positive, the voltage value obtained by multiplying the reference voltage by the positive voltage correction coefficient gp is supplied to the subtractor 51, and when the voltage of the reference sine wave is negative, A voltage value obtained by multiplying the reference voltage by the negative voltage correction coefficient gn is supplied to the subtractor 51 .

Note that, in the present embodiment, the correction coefficient setting unit 35 sets gp=1 and gn=1 when the voltage and current fluctuation phases are not opposite phases.

Therefore, in the present embodiment, when the fluctuation phase is the opposite phase, the waveform distortion of the AC component of the output voltage is suppressed by correcting the gain of the reference voltage instead of the proportional gain of the PI control.

<Fourth Embodiment>
Next, an image forming apparatus according to the fourth embodiment will be described. In the voltage generator 10b included in the image forming apparatus of the fourth embodiment, a power control unit 12b configured as shown in FIG. 18 is used instead of the power control unit 12 configured as shown in FIG. The power control unit 12b has a correction coefficient calculation unit 91 to which a current effective value storage unit 90 is added instead of the correction coefficient calculation unit 34. FIG. Other constituent parts are the same as in the first embodiment. Components similar to those of the first embodiment are denoted by the same reference numerals, and descriptions thereof are omitted.

The correction coefficient calculation unit 91 has a current effective value storage unit 90 in addition to the output impedance storage unit 34a, the first correction coefficient calculation unit 34b, and the second correction coefficient calculation unit 34c.

The current effective value storage unit 90 receives the positive current effective value Iprms and the negative current effective value Inrms from the positive current effective value calculation unit 31a and the negative current effective value calculation unit 31b, respectively. store the positive current rms value Iprms and the negative current rms value Inrms. The current effective value storage unit 90 stores the positive current effective value Iprms and the negative current effective value Inrms for one fluctuation period, respectively, in the first correction coefficient calculation unit 34b and the second correction coefficient calculation unit 34c for each fluctuation period. to enter. The fluctuation period is the period of load fluctuation, for example, the rotation period of the charging roller 3 described above.

In this embodiment, the first correction coefficient calculator 34 b calculates the first correction coefficient αp based on the positive current effective value Iprms input from the current effective value storage unit 90 . The second correction coefficient calculation unit 34 c calculates the second correction coefficient αn based on the negative current effective value Inrms input from the current effective value storage unit 90 .

The positive current effective value Iprms and the negative current effective value Inrms stored in the current effective value storage unit 90 are appropriately updated when the fluctuation phase changes.

In the present embodiment, since the current effective value storage unit 90 stores the positive current effective value Iprms and the negative current effective value Inrms, the first correction coefficient αp and the second correction coefficient αn can be calculated at high speed.

As a modified example of the second embodiment, it is possible to apply a correction coefficient calculation section to which a current peak value storage section is added, as in the present embodiment. The current peak value storage unit stores the positive current peak value and the negative current peak value for one fluctuation period, and inputs them to the first correction coefficient calculation unit 34b and the second correction coefficient calculation unit 34c.

In each of the above-described embodiments, the switching circuit included in the AC power supply 11a is configured as a half-bridge circuit, but the present invention is not limited to this, and the switching circuit may be configured as a full-bridge circuit.

Although the present invention has been described above based on each embodiment, the present invention is not limited to the requirements shown in the above embodiments. These points can be changed within the scope of the present invention, and can be determined appropriately according to the application form.

2 Photoreceptor 3 Charging Roller 4 Exposure Section 5 Developing Device 10, 10a, 10b Voltage Generator 11 Power Supply Section 11a AC Power Supply 11b DC Power Supply 12, 12a, 12b Power Control Section (Power Control Device)
30 voltage effective value calculation unit 31 current effective value calculation unit 31a positive current effective value calculation unit 31b negative current effective value calculation unit 31c addition unit 32 averaging unit 32a first averaging unit 32b second averaging unit 33 fluctuation phase determination unit 34 correction coefficient calculation unit 34a output impedance storage unit 34b first correction coefficient calculation unit 34c second correction coefficient calculation unit 35 correction coefficient setting unit 36, 36a voltage control unit 50 reference voltage generation unit 52, 52a proportional unit 53 integration unit 55 reference Sine wave generation unit 61 positive/negative determination unit 62 reference proportional gain storage unit 80 current peak value detection unit 80a positive current peak value detection unit 80b negative current peak value detection unit 90 current effective value storage unit 91 correction coefficient calculation unit 100 image forming apparatus

Japanese Patent Application Laid-Open No. 2004-102079

Claims (12)

A voltage generator that has a DC power supply and an AC power supply connected to the DC power supply, generates a voltage obtained by superimposing an AC voltage on a DC voltage, and applies the voltage to a rotating body,
Fluctuation of the voltage effective value calculated for each period of the voltage waveform of the output voltage of the AC power supply;
Either a current effective value calculated for each cycle of the voltage waveform of the output current of the AC power supply, or a current peak value obtained by adding a positive current peak value and a negative current peak value detected based on the current waveform of the output current. A fluctuation phase determination unit that determines whether or not the fluctuation of one of the
When the determination result by the fluctuation phase determination unit is the opposite phase, a proportional gain in PI control or a reference voltage is calculated from the positive current effective value and the negative current effective value calculated from the output current, and the fluctuation phase a voltage control unit that performs control to set the proportional gain or the reference voltage to a prescribed value when the determination result by the determination unit is not in reverse phase ;
A voltage generator having a an output impedance storage unit that stores output impedance;
a positive current effective value calculator that calculates the positive current effective value from the output current;
a negative current effective value calculator that calculates the negative current effective value from the output current;
a correction coefficient calculation unit that calculates a first correction coefficient based on the output impedance and the positive current effective value, and calculates a second correction coefficient based on the output impedance and the negative current effective value. ,
The voltage control unit performs gain correction using the first correction coefficient when the output voltage is positive when the determination result by the fluctuation phase determination unit is the opposite phase, and the output voltage is negative. 2. The voltage generator according to claim 1, wherein gain correction is performed using said second correction coefficient when a a voltage effective value calculation unit that calculates the voltage effective value from the output voltage;
3. The voltage generator according to claim 2, further comprising a current effective value calculation section for calculating the current effective value from the output current. The current effective value calculation unit calculates the current effective value by adding the positive current effective value calculation unit, the negative current effective value calculation unit, and the positive current effective value and the negative current effective value. 4. The voltage generator according to claim 3, comprising: a first averaging unit that averages the voltage effective value output from the voltage effective value calculation unit at regular intervals and outputs an average voltage effective value;
a second averaging unit for averaging the current effective value output from the current effective value calculating unit for each constant period and outputting an average current effective value;
The fluctuation phase determination unit determines a magnitude relationship based on the previous output value of the voltage effective value output from the voltage effective value calculation unit, and the previous output value of the current effective value output from the current effective value calculation unit. 5. The voltage generator according to claim 4, wherein it is determined that the fluctuation of the output voltage and the fluctuation of the output current are in opposite phases when the magnitude relationship with respect to the output value of is different. an output impedance storage unit that stores output impedance;
a positive current peak value detection unit that detects a positive current peak value from the output current;
a negative current peak value detection unit that detects a negative current peak value from the output current;
a correction coefficient calculation unit that calculates a first correction coefficient based on the output impedance and the positive current peak value, and calculates a second correction coefficient based on the output impedance and the negative current peak value. ,
The voltage control unit performs gain correction using the first correction coefficient when the output voltage is positive when the output voltage fluctuation and the output current fluctuation are in opposite phases, and the output voltage is positive. 2. The voltage generator according to claim 1, wherein gain correction is performed using said second correction coefficient when is negative. The voltage control unit includes a reference sine wave generation unit that generates a reference sine wave for controlling the AC power supply, and a positive/negative determination unit that determines whether the reference sine wave generated by the reference sine wave generation unit is positive or negative. wherein gain correction is performed using the first correction coefficient when the reference sine wave is positive, and gain correction is performed using the second correction coefficient when the reference sine wave is negative. 3. The voltage generator according to 2. 3. The voltage generator according to claim 2, further comprising a current effective value storage unit for storing the positive current effective value and the negative current effective value for a predetermined period and inputting them to the correction coefficient calculating unit. 9. The voltage generator according to any one of claims 1 to 8, wherein said AC power supply has a switching circuit configured by a half bridge circuit or a full bridge circuit. A power supply control device having a DC power supply and an AC power supply connected to the DC power supply, and controlling a power supply unit that generates a voltage obtained by superimposing an AC voltage on a DC voltage and applies it to a rotating body,
Fluctuation of the voltage effective value calculated for each period of the voltage waveform of the output voltage of the AC power supply;
Either a current effective value calculated for each cycle of the voltage waveform of the output current of the AC power supply, or a current peak value obtained by adding a positive current peak value and a negative current peak value detected based on the current waveform of the output current. A fluctuation phase determination unit that determines whether or not the fluctuation of one of the
When the determination result by the fluctuation phase determination unit is the opposite phase, a proportional gain in PI control or a reference voltage is calculated from the positive current effective value and the negative current effective value calculated from the output current, and the fluctuation phase and a voltage control unit that performs control to set the proportional gain or the reference voltage to a specified value when the determination result by the determination unit is not in reverse phase . a voltage generator according to any one of claims 1 to 9;
a charging roller as the rotating body to which the voltage output from the voltage generator is applied;
a photoreceptor arranged in proximity to the charging roller;
An image forming apparatus having A control method for a power supply unit that includes a DC power supply and an AC power supply connected to the DC power supply, generates a voltage obtained by superimposing an AC voltage on a DC voltage, and applies the generated voltage to a rotating body,
Fluctuation of the voltage effective value calculated for each period of the voltage waveform of the output voltage of the AC power supply;
Either a current effective value calculated for each cycle of the voltage waveform of the output current of the AC power supply, or a current peak value obtained by adding a positive current peak value and a negative current peak value detected based on the current waveform of the output current. Determine whether or not the fluctuation of one of the and is in opposite phase,
When the determination result is the opposite phase, the proportional gain in PI control or the reference voltage is calculated from the positive current effective value and the negative current effective value calculated from the output current, and when the determination result is not the opposite phase, the proportional A control method that controls a gain or a reference voltage to a specified value .

Images